Electrodeposition of bright nickel



United States Patent 3,008,883 ELECTRODEPOSITION 0F BRIGHT NICKEL Frank Passal, Detroit, Mich., assignor to Metal & Thermit Corporation, Woodbridge Township, N.J., a corporation of New Jersey No Drawing. Filed Nov. 30, 1959, Ser. No. 855,968 13 Claims. (Cl. 20449) This invention relates to electroplating nickel and more particularly to the electrodeposition of bright nickel. This application is a continuation-in-part of patent application Serial No. 781,202, filed December 18, 1958, now

abandoned.

Nickel electrodeposits as plated from Watts, high chloride, fluoborate, etc., type baths are not bright when plated in thicknesses substantially greater than those of very thin strike or flash coatings. Such deposits do not increase in luster with increasing thickness but rather decrease in brightness until dull matte deposits are obined. To obtain bright deposits from such baths in substantial thickness, it is necesssary to add certain additives, commonly of organic nature, which in cooperation produce highly lustrous deposits with good rate of brightening. It is a common characteristic of such so-c-alled bright-nickel plating baths that the deposits tend to increase in luster with increasing thickness. The practical advantage of these bright-nickel baths is that bright deposits can be obtained on basis metal which have not been polished or which do not have a high starting luster, within reasonable specification thicknesses of nickel. Other concomitant advantages such as, leveling or the ability of the deposits to fill in pores, scratches or other superficial defects of the basis metal, may also be obtained.

Addition agents useful as brighteners in nickel plating baths are generally divided into two classes on the basis of their predominant function. Primary brighteners are materials used in very low or relatively low concentration, such as 0.002 to 2 g./l., and which by themselves may or may not produce any visible brightening action. Those primary brighteners which may exhibit some brightening effects generally also produce deleterious side effects such as reduced cathode efliciency, poor deposit color, deposit brittleness and exfoliation, very narrow bright plate range, or failure to plate any nickel at all on the low current density areas. Secondary brighteners are materials which are ordinarily used in app-reciably higher concentrations, such as 1 to 30,g./l., than primary brighteners. These materials, by themselves, may produce some brightening or grain refining effects, but the deposits are not usually mirror bright and the rate of brightening is usually inadequate.

Ideally, when primary and secondary brighteners of properly chosen and compatible nature are combined, fully bright, ductile deposits over a wide current density range are obtained which exhibit a good rate of brightening. This rate of brightening may vary from low, medium to high, with the latter preferred where maximum luster is desired with a minimum of thickness of nickel applied. Similarly, the rate of leveling may vary from low, medium to high, depending on the particular cooperating additives chosen. The concentrations of the secondary brighteners may vary within fairly wide limits, i.e., their concentrations are not usually critical. The concentrations of the primary brighteners must usually be maintained within fairly narrow limits in order to maintain such desirable deposit properties as good duc tility, adequate low current density coverage, etc. Any bright nickel system which can be made less critical or more tolerant to fluctuations in primary brightener con- 3,008,883 Patented Nov. 14, 1961 centrations will have obvious advantages, particularly since the low concentrations of primary'brighteners and the intrinsic chemical nature of some make strict control by chemical analysis difficult. Any material of primary brightener nature or eifectiveness which can be used over fairly wide limits of concentrations is of great value in bright nickel plating.

I have now discovered a new class of primary brightencrs which possess advantages over those previously known.

It is an object of this invention to provide an efiicient process for electrodepositing bright and smooth nickel deposits.

Another object of this invention is to provide bath compositions for nickel plating from which bright nickel electrodeposits are obtained.

The invention also contemplates providing novel primary brighteners for use in nickel plating baths.

The invention contemplates electrodepositing nickel from nickel-containing baths to which have been added a secondary brightener and a small but effective amount of a novel primary bn'ghtener selected from a class of organic compounds having the following general structure:

wherein N l and N i group, and in the group, to a carbon atom alpha or gamma to the nitro gen atom in the same ring.

Of the compounds of the type encompassed by the general formula, those that are in the doubly quaternized form, i.e., a and 0 equal 1, are preferred. These doubly quaternary nitrogen compounds are prepared by reacting the singly quaternized compound containing a tertiary nitrogen atom, e.g., the pyridine derivative, with an alkylating agent such as dimethylsulfate. These quaternary compounds may be used per se, or the anionic functional group may be replaced by other anions. The anions are from water-soluble acids or water-soluble salts. This is illustrated in the replacement of the chloride anion by the acetate anion; by reacting the chloride-containing quaternary with silver acetate. Among the common anions useful in the invention are bromide, chloride, iodide, sulfate, methosulfate, ethosulfate, chloroacetate, citrate, and perchlorate. The iodides, bromides, methosulfates and ethosulfates are preferred because of their solubility and compatibility in the nickel plating baths.

Compounds of this class which have been found to be effective as primary brighteners are the following:

TABLE I 1-(2-quinoly1methyl) pyridinium iodide.

. l-(2-quinolylmethy1) pyridinium bromide.

1-( 2=quinolylmethyl)-3-picolinium iodide.

. 1- 2-quinolylmethyl)-3-picolinium bromide.

2'(2-quinolylmethyl) isoquinolinium iodide.

2-(2-quinolylmethyl) isoquinolinium bromide.

. 4-methyl-2- (2-quinolylmethyl) isoquinolinium iodide.

. 4-methyl-2 Z-quinolylmethyl) isoquinolinium bromide.

I. 1-(4-quinolylmethyl) pyridinium iodide.

J. 2-(4-quinolylmethyl) isoquinolinium iodide.

K. 4-methyl-2*(4-quinolylmethyl) isoquinolinium iodide.

L. 1-[2- (6-methylquinolyl) methyl] pyridinium iodide.

. 2-[2-(6-methylquinolyl) methyl] isoquinolinium iodide.

. 4-methyl-2 -[2-(6-methylquinolyl) methyl] -isoquinoli'riium iodide.

. l-(l-isoquinolylmethyl) pyridinium iodide.

1-( l-isoquinolylmethyl) -3-picolinium iodide.

. d-Pyridinium-l-methylquinaldinium diiodide, otherwise named l-(2-quinolylmethyl) pyridinium iodide methoiodide.

. a-Pyridinium-l-methyllepidinium diiodide, otherwise named 1-(4-quinolylmethyl) pyridinium iodide methoiodide.

u-Pyridinium-l-methylquinaldinium diiodide.

a-Pyridinium-l=methyl-2-picolinium diiodide.

a-Pyridinium-l-methylquinaldinium dimethosulfate.

a-Pyridinium-l ethylquinaldinium diethosulfate.

a-(Pyridinium iodide) -l-methylquinaldinium methosulfate.

a 0 2 a mozweo S. T. U. V. W.

The novel class of primary brighteners of this invention when used in combination with suitable secondary brighteners giv'e brilliant bright nickel deposits which have excellent ductility, low current density coverage, rate of brightening and leveling characteristics. Of particular advantage are the wide usable concentration limits of these novel primary brighteners without adversely affecting the low current density coverage and ductility of the deposits.

Another outstanding advantage is that these novel primary brighteners, in contrast to most of the primary brighteners of the prior art, are subject to analytical control. This ease of analytical control is due to the active methylene (CH group which in alkaline media gives intense color reactions with such reagents as chloranil, picryl chloride and sodium 1,2 naphthoquinone-4-su1fonate. These intense colors can be measured for their intensity at suitably chosen wave lengths by use of a spectrophotometer or colorimeter, and the concentrations in the nickel plating baths can then be calculated. This case of analytical control facilitates the calculation of suitable replenishment additions to make up for losses due to electrolysis, drag-out or adsorption by such materials as anode carbon, tank linings, etc.

Another advantage of this novel class of primary brighteners is that they can be readily synthesized from relatively cheap and easily available materials.

The primary brighteners of this invention are used in concentrations of from 0.002 to 0.250 gram per liter, the particular concentration chosen depending on the particular type and concentration of secondary brightener used and also on such factors as the degree of luster,

pounds as 1,3,6-naphthalene trisulfonate, sodium or potassium salts of saccharin, the sodium or potassium salts of ortho-sulfobenzaldehyde, the water soluble aryl sulfonic acid and sulfinic acid compounds, etc. For use in high chloride type nickel plating baths, a preferred secondary brightener is a sodium or potassium salt of sulfonated dibenzothiophene dioxide. This sulfonated dibenzothiophene dioxide is prepared by sulfonating diphenyl with fuming sulfuric acid (20% oleum) for about 2 hours, isolating and neutralizing. The predominant reaction product is believed to be the compound containing three sulfonic acid groups. However, the monoand di-substituted components are also believed present. The secondary brighteners are generally characterized by having at least one sulfone or sulfonic acid group attachedi to a nuclear carbon.

Auxiliary secondary brighteners such as 2-butene 1,4 diol and N-vinyl-2-pyrrolidone, may be used in con-- junction with the secondary brightener. These auxiliary secondary brighteners act to accentuate deposit luster, to extend the life of secondary brighteners and to increase leveling characteristics of the deposits.

Conventional baths and processes for electroplating bright nickel are described in Principles of Electropla ing and Electroforming, Blum and Hogaboom, pag 362-381, revised third edition, 1949, McGraw-Hill Book Co., Inc, New York; and in Modern Electroplating, edited by A. G. Gray, the Electrochemical Society, 1953, pages 299-355. The control and operating conditions, including the concentration of the bath ingredients, pH, temperature, cathode current density, etc., of these conventional baths are generally applicable to the present invention. Practically all baths for electroplating bright nickel contain nickel sulfate, a chloride, usually nickel chloride; a buffering agent, usually boric acid; and a wetting agent, e.g., sodium lauryl sulfate, sodium lauryl ether sulfate, and sodium 7-ethyl-2-methyl-4-undecanol sulfate. Such baths include the well-known Watts bath and the high chloride bath. Other baths may contain, as the source of the nickel, a combination of nickel fluoborate with nickel sulfate and nickel and chloride, or a combination of nickel fluoborate with nickel chloride. Typical Watts-type baths and high chloride baths are noted in Tables II and 1H.

TABLE II Watts-type baths Nickel sulfate 200 to 400 g./l. Nickel chloride 30 to 75 g./l. Boric acid 30 to 50 g.'/l. Temperature to F. Agitation. pH 2.5 to 4.5 electrometric.

TABLE III High chloride baths Nickel chloride 150 to 300 g./l. Nickel sulfate 40 to 150 g./l. Boric acid 30 to 50 g./l. Temperature 100 to 150 F. Agitation. pH 2.5 to 4.5 electrometric.

Best plating results are usually achieved in the electrodeposition process when a method of preventing the thin film immediately adjacent the cathode from becoming depleted in'cation content, is utilized. This is desirably accomplished by agitation, such as air agitation, solution pumping, moving cathode rod, etc. 1 For the purpose of giving those skilled in the art a 1 better understanding of the invention, illustrative examples are given. In each of the examples, an aqueous acidic nickel containing bath was made up with the specified components. Electrodeposition of nickel was carried out by passing electric current through an electric circuit comprising an anode and sheet metal or rod cathode, both immersed in the bath. The baths were agitated, usually by a moving cathode. Bright electrodeposits were obtained in all the tests included herein as examples.

In Examples 1 through 13, the following standard 5 bath was used as a base solution:

G./l. N ckel snalfa to 300 Nlckel chlorid 60 Bonc acid 45 Sodium lauryl s lf 0.5 The pnmary brightener 1s identified from Table I.

TABLE IV Example Additives Amt., .D., pH Temp, No. g./l. a.s.f. F.

sodium 1,3,6-naphthalene 1 trisulfonate.

Primary Brightener A 0.05 35 3.0 130 20 sodium 1,5-naphthalene di- 10 sulfonate. Primary Brightener B 0. 08 35 3.0 130 sulfonated dibenzothiophene 4 dioxide. Primary Brightener A 0.06 35 3. 0 130 o-sulfobenzaldehyde (Na 3 salt). Primary Brightener D 0.05 3. 5 135 {saccharin (as K salt) 4 Primary Brightener H 0.10 3. 8 140 saeeharin (as K salt)- 2 p-toluene sulfonamide 2 Primary Brightener K. 0. 06 40 4.0 140 benzene sulfonamide 2 39 7 saccharin (as K salt) 2 Primary Brighteuer Q, 0.05 30 3. 8 135 sodium 1,3,6-naphthalene 20 8 trisulfonate.

2-butene 1,4 diol 0.2 Primary Brightenor A 0. 05 sodium 1,3,6-naphthalene 20 9 trisulfonate.

N-vinyl-2-pyrrolidone 1 Primary Brightener D 0. 06 10 {saccharin (K salt) 4 Primary Brightener S 0.02 11 {Saccharin (K salt) 4 Primary Brightener U. 0.04 12 {saccharin (K salt) 4 Primary Brightener 0.05 saccharin (K salt)... 2 13 p-toluene sulfonamide 2 Primary Brightener T 0.04

In Examples 14 to 21 inclusive, the following standard bath was used as a base solution:

Nickel chlor 250 Nickel sulfat 45 Boric acid 45 Sodium lauryl sulfate 0.5

TABLE V Example Additives Amt, O.D., pH Temp,

No. g./l. a.s.f. F.

14 {saecharin (K salt) 4 Primary Brightener A- 0.08 45 3. 5 140 saecharin (K salt) 4 15 p-tolueue sulfonamide 2 Primary Brightener B 0. 08 45 3. 5 140 sulfonated dibenzothiophene 4 16 dioxide.

Primary Brightener C 0.05 45 3. 5 140 sulfonated dibenzothiophene 4 17 dioxide.

Primary Brightener E 0. 06 45 3. 5 140 sulfonated dibenzothiophene 2 18 dioxide. 5

""" saceharin (K salt). 2 Primary Brightener A 0. 08 45 3. 5 140 19 {saeeharin (K salt) 4 Primary Brightener U 0.065 40 4.0 140 sulfonated dibeuzothiophene 4 20 dioxide.

Primary Brightener U 0.065 40 3. 5 130 21 {saceharin (K salt) 4 Primary Brightener T- 0. 01 40 4. 0 140 The foregoing examples illustrate specific baths and processes, several being preferred. It is understood that the compositions and conditions may be varied. Al-

though the potassium salts were most often used and are preferred, they may be partially or completely replaced by such other salts as the sodium salts, etc.

The nickel electrodeposits obtained from baths utilizing the novel brightener combination are advantageous in that mirror-bright lustrous electrodeposits having a high degree of ductility are obtained over a wide range of current densities. The bright nickel electrodeposits are preferably plated on a copper or copper alloy basis metal. However, they may be electrodeposited directly on such metals as iron, steel, etc.

As many embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention includes all such modifications and variations as come within the scope of the appended claims.

I claim:

1. A process for electroplating mirror-bright nickel from an aqueous acid nickel electroplating bath containing a secondary brightener and between 0.002 g./=1. and 0.25 g./1. of a primary brightener, said primary brightener being a compound having the structure are each selected from the class consisting of pyridine, quinoline and isoquinoline; R, R and R" are each selected from the class consisting of alkyl groups having 1 to 4 carbon atoms; X and X are anions; a, b, c and d are each 0 to 1; and wherein the methylene group is bonded to the nuclear nitrogen of the wherein group, and in the are each selected from the class consisting of pyridine, quinoline and isoquinoline; R, R and R" are each selected from the class consisting of alkyl groups having 1 to 4 carbon atoms; X and X are anions; a and c are l, and b and d are each 0 to 1; and wherein the methylene group is bonded to the nuclear nitrogen of the wherein group, and in the wherein DO and N i are each selected from the class consisting of pyridine, quinoline and isoquinoline; R, R and R"'are each selected from the class consisting of alkyl groups having 1 to 4 carbon atoms; X and X are anions selected from the class consisting of chloride, bromide, iodide, ethosulfate and lmethosulfate; a and c are l, and b and d are each to 1; and wherein the methylene group 'is bonded to the nuclear nitrogen of the group, to a carbon atom alpha or gamma to the nitrogen atom in the same ring.

4. A process for electroplating mirror-bright nickel from an aqueous acid nickel electroplating bath containing between 0.01 g./l. and 0.1 g./1. of a primary brightener, said primary brightener being a compound group, and in the having the structure N i and N are each selected from the class consisting of pyridine, quinoline and isoquinoline; R, R and R" are each selected from the class consisting of alkyl groups having 1 to 4 carbon atoms; X and X are anions selected from the class consisting of chloride, bromide, iodide, ethosulfate, and methosulfate; a and c are 1, and b and d are each 0 to 1; and wherein the methylene group is bonded to the nuclear nitrogen of the group, to a carbon atom alpha or gamma to the nitrogen atom in the same ring; and between 1 g./ 1. and 20 g./l.

wherein group, and in the of a secondary brightener selected from the class consisting of the sodium and potassium salts of sacchanin, :sulfonated dibenzothiophene dioxide, and 1,3,6-naphthalene trisulfonate.

5. An aqueous acid electrolytic bath containing soluble nickel salts for the electrodeposition of rnirror-bright nickel containing a secondary brightener and between 0.002 -g. /l. and 0.25 g./l. of -a primary brightener, said primary brightener being a compound having the structure wherein N i and N are each selected from the class consisting of pyridine, quinoline and isoquinoline; R, R vand R" are each selected from the class consisting of alkyl groups having 1 to 4 carbon atoms; X and X are anions; a, b, c and d are each 0 to 1; and wherein the methylene group is bonde to the nuclear nitrogen of the group, to a carbon atom alpha or gamma to the nitrogen atom in the same ring.

6. An aqueous acid electrolytic bath containing soluble nickel salts for the electrodeposition of mirror-bright nickel containing between 0.01 g./l. and 0.1 g./1. of a primary brightener, said primary brightener being a compound having the structure group, and in the wherein N and 'N are each selected from the .class consisting of pyridine, quinoline and isoquinoline; R, R and R" are each selected from the class consisting of alkyl groups having 1 to 4 carbon atoms; X and X are anions selected from the class consisting of chloride, bromide, iodide, ethosulfate, and methosulfate; a and c are 1, and b and d are each 0 to l; and wherein the methylene group is bonded to the nuclear nitrogen of the group, to a carbon atom alpha or gamma to the'nitrogen atom in the same ring; and between 1 g./l. and 20.g./l. of a secondary brightener selected from the class consisting of the sodium and potassium salts of saccharin,

group, and in the 'sulfonated dibenzothiophene dioxide, and 1,3,6-naphthalene trisulfonate.

7. The-bath of claim 6 in which the primary brightener is 1-(2-quinolylmethy1) .pyridinium iodide.

8. The bath of claim 6 in which the primary brightener 13. The bath of claim 6 in which the primary brightener is a-pyridinium-l-methylquinaldinium diiodide. is 0: (pyridinium iodide)-1-methylquinaldinium metho- 9. The bath of claim 6 in which the primary brightener sulf te. is a-pyridimium-l-methyl-2-picolinium diiodide.

10. The bath of claim 6m which the primary brightener 5 References Cited in the file of this patent is a-pyridinium-l-methylquinaldinium dimethosulfate.

11. The bath of claim 6 in which the primary brightener UNITED STATES PATENTS is I-(Z-quinolylmethyl)-3-picolinium iodide. 2,513,280 Brown July 1950 12. The bath of claim 6 in which the primary brightener 2,644,789 Shenk July 7, 1953 is 2-(2-quino1ylmethy1) isoquinolinium iodide. 10 2,654,704 Brown et a1 Oct. 6, 1953 

1. A PROCESS FOR ELECTROPLATING MIRROR-BRIGHT NICKEL FROM AN AQUEOUS ACID NICKEL ELECTROPLATING BATH CONTAINING A SECONDARY BRIGHTENER AND BETWEEN 0.002 G./L. AND 0.25 G./L. OF A PRIMARY BRIGHTENER, SAID PRIMARY BRIGHTENER BEING A COMPOUND HAVING THE STRUCTURE WHEREIN 